A knocking sensor for detecting knocking in an engine is disposed in the cylinder block of an internal combustion engine. An inspection apparatus for inspecting whether such a knocking sensor normally operates or not before an engine is set in a vehicle is conventionally unavailable, though Japanese Patent Laid-Open No. 5-26778 is a conventional document describing an apparatus for detecting abnormality of a knocking sensor.
In conventional engine tests, a continuity test and a diagnosis test for an engine computer are available as a test for a knocking sensor. The continuity test judges whether a sensor is normal by measuring a value of resistance across sensor terminals. The diagnosis test judges whether a sensor is normal by using the output results of failure diagnosis on an engine computer.
However, the continuity test is a one-sided test merely judging whether a value of resistance of a knocking sensor is normal. Thus, an actually measured value may not be properly outputted. Further, in the diagnosis test, a measurement is performed by a knocking sensor in a motoring state in which an engine is ignition operated or a crankshaft and a piston are driven by an external electric motor via an output shaft. An outputted detection vibration value of the knocking sensor may not be constant and is susceptible to disturbance.
According to the conventional document, in the event of an abnormal condition in a knocking sensor when an engine is used, the signal of the knocking sensor is processed, and a standard deviation and an abnormality decision value are compared with each other to decide abnormality of the knocking sensor. When this method is used in a tester for an engine, the decision process becomes extremely complicated.
An object of the present invention is to provide a method and apparatus for inspecting a knocking detector whereby the above-described problem is solved, a constant vibration detection value can be obtained without being affected by disturbance, and whether the knocking detector normally operates is quantitatively decided with ease.